A rotor of a traditional brushless motor is illustrated in FIG. 11. The rotor 20 comprises a shaft 21, a rotor core fixed onto the shaft 21, magnets 23 mounted to a radially outer surface of the rotor core, and a keeper ring 26 to retain the magnets 23 on the rotor core against centrifugal force. The keeper ring 26 is usually made of stainless steel and has to be very thin, for example less than 0.2 mm thickness, or else the performance of the motor will be significantly decreased. Therefore tooling is needed, tolerance control must be strict, and the production cost is high.
Additional metal discs 24 and 25 are provided on each end of the rotor core, and the rotor is balanced by drilling holes 27 in the discs. The discs are usually made of copper which is expensive.
There is a desire for a lower cost micro brushless motor which is at least just as reliable.